Effects of rotation tillage on available nutrients and structural characteristics of dissolved organic carbon of Fluvo-aquic soil in northern Henan Province

Tillage is an important practice for improving soil quality. The effects of tillage on soil nutrient contents are well known. However, the understanding of the effects of tillage on soil dissolved organic carbon (DOC) and its structure is rare. This study aimed to select optimum tillage mode by exploring the effect of tillage mode on DOC and its structure in Fluvo-aquic soil in northern Henan Province. A field experiment was carried out using five treatments designed with different tillage rotation modes during the wheat season. The treatments were as follows: 1) continuous rotary tillage (RT-RT-RT); 2) deep tillage-rotary tillage-rotary tillage (DT-RT-RT); 3) deep tillage-rotary tillage-strip rotary tillage (DT-RT-SRT); 4) deep tillage-strip rotary tillage-strip rotary tillage (DT-SRT-SRT); 5) deep tillage-strip rotary tillage-rotary tillage (DT-SRT-RT). The contents of alkaline hydrolysis nitrogen (AN), available phosphorus (AP), available potassium (AK), DOC, degree of humification, molecular weight and polymerization degree of organic matter, proportion of hydrophobic components, degree of aromatization and molecular weight of soil were measured and analyzed. The results showed that the difference in all the indexes among treatments was mainly demonstrated in the 0–40 cm soil layer. Compared with those under RT-RT-RT in the 0–40 cm soil layer, the AN, AP, and AK increased by 17.8%, 17.2%, and 19.6% (P<0.05), respectively, under DT-SRT-RT, whereas the DOC content, degree of humification, and proportion of hydrophobic components increased by 20.2%, 53.1%, and 27.4% (P<0.05), respectively, under DT-SRT-RT. Compared with those under RT-RT-RT, the aromatization degree and molecular weight in the 20–30 cm soil layer increased by 21.0% (P<0.05), and the molecular weight and polymerization degree of organic matter in the 10–30 cm soil layer decreased by 36.7% (P<0.05) under DT-RT-SRT. Available soil nutrients and DOC and its structural characteristics were affected by soil depth, tillage mode, and the interaction between soil depths and tillage modes. The correlation among different indices decreased with increasing soil depth. In summary, compared with continuous rotary tillage, DT-SRT-RT improved soil available nutrients and DOC content and increased the complexity of the DOC structure. Therefore, the DT-SRT-RT mode was suggested as a suitable rotation tillage mode in the Fluvo-aquic soil areas of northern Henan.